Resin seal ring and manufacturing method

ABSTRACT

The present invention provides a seal ring which can be prevented from being broken by an expansion and a shock applied thereto when the seal ring is fitted on a rotary shaft and does not have a configurative disadvantage such as a burr. Therefore no post-processing is required. The present invention also provides materials of the seal ring and a method of manufacturing the seal ring. The seal ring is made of resin and having two abutments confronting each other and a gate mark formed in an injection molding operation.

This application is a divisional application of Ser. No. 10/856,398,filed May 27, 2004, which claims the priority of Japanese ApplicationsSerial Nos. P2003-152219, filed May 29, 2003 and P2003-420450, filedDec. 18, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to a resin seal ring by injection molding,which is used for a hydraulic mechanism of an automatic transmission(AT), a continuously variable transmission (CVT) and a method ofmanufacturing the seal ring. More particularly, the present inventionrelates to a small seal ring, having an inner diameter not more than 20mm, which can be incorporated in a mating shaft with a high mountabilityand a method of manufacturing the seal ring.

Nowadays an oil-sealing ring for sealing a hydraulic oil used much inthe automatic transmission and the continuously variable transmission isformed by injection-molding a mixture of polyether ketone resin, areinforcing component such as carbon fiber, a solid lubricant such aspolytetrafluoroethylene (PTFE) resin, and the like. An abutment portionconsisting of adjacent abutments is formed on the oil-sealing ring bycutting a portion thereof. Agate into which resin is injected is formedat a portion (mainly on inner peripheral surface) opposed to theabutment portion disposed at the center of the seal ring. The seal ringis fitted on a rotary shaft by expanding the abutments with a jig.

A known method of fitting the resin seal ring on a mating shaft(hereinafter referred to as merely shaft) is described below withreference to FIG. 4.

A resin seal ring 1 is fitted on a mating shaft 11 by using a taperedjig 4 as follows: After the seal ring 1 is fitted on the tapered jig 4from a small-diameter side 4 a thereof to a large-diameter side 4 bthereof, the shaft 11 is inserted into the tapered jig 4. Thereafter theseal ring 1 is dropped into a seal ring-mounting groove 12 of the shaft11 from the large-diameter side 4 b of the tapered jig 4.

In fitting the seal ring ion the shaft 11, a strain is generated in theneighborhood of the position of the seal ring opposed to the abutmentportion and a stress concentration occurs. Therefore when the seal ring1 has a gate for injection molding use or a weld portion having a lowmechanical strength at the position opposed to the abutment portion, theseal ring may be broken at the position opposed to the abutment portion.Another problem of the seal ring having the gate for the injectionmolding use at the position opposed to the abutment portion is that theorientation of reinforcing fibers such as carbon fibers disposed in thevicinity of the gate is parallel with the direction of a strain-causedcrack. Thus it is impossible to obtain a sufficient reinforcing effectin the neighborhood of the gate. Therefore when the seal ring is fittedon the shaft, the seal ring is broken at the gate mark. In recent years,there is a tendency for the seal ring to be formed compactly because ahydraulic mechanism is becoming compact. The seal ring having an innerdiameter of 20 mm or less is easily broken even though the seal ring iscomposed of a comparatively flexible material. Polyether ketone resin isknown as a crystalline thermoplastic resin excellent in its heatresistance, mechanical property, self-lubricant property, andflexibility. The above-described problem of breakage is caused bydeterioration of flexibility of the composition of the seal ringcontaining an inorganic reinforcing material such as carbon fibers whichimpart a demanded high wear resistance to the seal ring.

As a means for solving the above-described problems, resin is injectedinto a portion in the vicinity of one end of abutments of the seal ringdisclosed in Japanese Patent Application Laid-Open No. 8-233110. In themethod disclosed in Japanese Patent No. 3299419, the gate position isspaced at a certain interval from the position opposed to the abutmentportion to prevent breakage of the seal ring.

However, the step cut portion is complicated in its configuration anddemanded to have high precision to keep oil-sealing performance. Thus atelescopic construction is adopted for the step cut portion. Therefore aparting line which may cause generation of a burr is present on theperiphery of the step cut portion. In the seal ring disclosed inJapanese Patent Application Laid-Open No. 8-233110, the gate to which ahighest pressure is applied is disposed on the periphery of the step cutportion when molding operation is performed. Thus the burrs tend to begenerated there.

In the seal ring disclosed in Japanese Patent No. 3299419, after theseal ring having the gate formed at a position spaced from the positionopposed to the abutments, the abutment portion is formed by a mechanicalprocessing as the means for avoiding breakage of the seal ring when itis fitted on the rotary shaft. However, the seal ring has the weldportion having a low strength. If the inner diameter of the seal ring isnot more than 20 mm, the weld portion is liable to be broken by a shockapplied to the seal ring when it is fitted on the rotary shaft.Supposing that the angle of the abutment portion of the seal ring is 180degrees and the angle of the portion opposed to the abutment portion is0 degree, the gate is disposed in the range of 45 to 90 degrees.However, the gate is not spaced sufficiently from the position where alarge strain is generated when the seal ring is fitted on the rotaryshaft. Thus the seal ring does not have any effect of improvingfittability of the seal ring on the rotary shaft or has deterioratedfittability.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-describedproblems. Therefore, it is an object of the present invention to providea resin seal ring which is flexible to such an extent that the seal ringis not broken when an expansion and a shock is applied to the seal ringin fitting the seal ring on a rotary shaft. It is another object of thepresent invention to provide a resin seal ring not having a weld portionthat is generated in a molding operation. It is still another object ofthe present invention to provide a resin seal ring not havingconfigurative disadvantages that a burr is formed and thatpost-processing is required. It is still another object of the presentinvention to provide a method of manufacturing the seal ring.

To achieve the object, the present invention provides a resin seal ringhaving two abutments confronting each other. When an inner diameter ofthe seal ring is expanded, with the seal ring being supported by threepoints consisting of the two abutments and by a position opposed to thetwo abutments, a thickness of a predetermined region in which a strainis generated in a higher magnitude than a strain generated in theposition opposed to the two abutments is set smaller than that of theposition opposed to the two abutments, with an outer diameter of theseal ring maintained.

Because the seal ring is thinned with the outer diameter of the sealring maintained, i.e., because the seal ring is thinned by expanding theinner diameter of the seal ring, the sealing performance of the sealring does not deteriorate. The amount of a strain generated in the thinportion decreases. Consequently it is possible to increase the expansionamount of the inner diameter of the seal ring.

Since the thin portion is formed, the energy stored in the seal ringdecreases when the seal ring is expanded. Consequently a smaller impactforce is applied to the seal ring when the seal ring is fitted on ashaft. Thereby it is possible to prevent an impact force from breakingthe seal ring.

The resin seal ring of the present invention includes abutmentsconfronting each other and a mark of a gate formed in an injectionmolding operation at a position spaced at a certain interval from aposition opposed to the abutments abutting each other. The gate mark ispresent in a range of not less than 90 degrees nor more than 180 degreesin a central angle of the seal ring with respect to the position opposedto the abutments, supposing that an angle of the position opposed to theabutments is 0 degree.

The method of manufacturing a resin seal ring having abutmentsconfronting each other, including a molding preparing step, an injectionmolding step, and a molded product take-out step. The injection moldingstep is performed by using a die having a resin reservoir providedthrough an inlet portion thereof at a position between a gate, forinjection molding use, which is spaced at a given interval from aposition opposed to an abutment portion and one abutment nearer to thegate than another abutment in a circumferential distance of the sealring. The inlet portion of the resin reservoir is configured so that aresistance to a flow of a resin into the resin reservoir is higher thana resistance to a flow of the resin into a sealing portion in aninjection molding operation; and a size of the resin reservoir is so setthat the resin reservoir and the sealing portion are chargedsimultaneously and completely with the resin in the injection moldingoperation.

The gate is spaced by not less than 90 degrees from the position opposedto the abutment portion. The size of the resin reservoir and theconfiguration of the inlet portion of the resin reservoir are adjustedin such a way that the resin reservoir and the sealing portion arecharged simultaneously and completely with resin or in such a way thatwhen the sealing portion is completely charged with the resin, the resinreservoir portion is incompletely charged therewith. Therefore in theseal ring of the present invention, it is possible to suppressgeneration of a burr formed by over-charging of resin and generation ofa molding sink that is generated by shortage of a follow-up pressure.Further the seal ring does not have a weld portion having a lowstrength. Thus the seal ring is excellent in its mechanical strength anddimensional precision. Therefore the seal ring can be prevented frombeing broken when it is expanded to fit it on a shaft.

The resin seal ring having abutments confronting each other is formed bymolding a resin composition. The resin composition contains a polyetherketone resin and a spherical carbon material, containing carbon as amain constituent element thereof, which is added to the polyether ketoneresin.

Owing to the use of the resin composition containing the polyetherketone resin and a predetermined amount of the spherical carbon materialadded thereto, the seal ring of the present invention has an excellentflexibility of the polyether ketone resin and in addition a low frictioncoefficient and an excellent wear resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional view in a diametrical direction showing a stateof a seal ring whose inner diameter is expanded.

FIG. 1B is a sectional view taken along a line B-B of FIG. 1A.

FIG. 2 is a graph showing the magnitude of a strain generated in theseal ring.

FIG. 3A is a plan view showing an example of a resin seal ring.

FIG. 3B is a sectional view taken along a line A-A of FIG. 3A.

FIG. 4 is a squint-eyed view showing a method of fitting the seal ringon a mating shaft.

FIG. 5 is a plan view showing one embodiment of the resin seal ring ofthe present invention.

FIG. 6 is a process chart showing the method of manufacturing the resinseal ring of the present invention.

FIG. 7 is a plan view showing one embodiment of the resin seal ring ofthe present invention.

FIG. 8 is a graph showing the relationship between an average particlediameter (μm) of a spherical carbon material and a mixing amount (volume%) thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By using a finite element method, the present inventors have analyzedthe construction of the seal ring by examining the amount of a straingenerated in the seal ring in fitting the seal ring on a mating shaft(hereinafter referred to as merely shaft) by expanding the innerdiameter of the resin seal ring having a constant thickness, by using atapered jig shown in FIG. 4. As result, they have found that when thetapered jig is used, the seal ring is supported on the peripheralsurface of the tapered jig at three points, namely, two abutmentsthereof and a position thereof opposed to the abutments. They have alsofound that the magnitude of a strain generated in a region is largerthan that of a strain generated at the position opposed to the abutmentswhere a gate is disposed. Therefore by making the thickness of theregion smaller than that of the gate, the region is expanded when aforce is applied to the seal ring. Thereby it is possible to prevent theseal ring from being broken at the gate formed at the central portion ofthe seal ring.

As a result of experiments based on the analysis of the construction ofthe seal ring, the present inventors have found the following fact:Supposing that the angle of the abutment portion of the seal ringconsisting of two abutments is 180 degrees and that the angle of theposition opposed to the abutment portion is 0 degree, it is possible toprevent the seal ring from being broken at the gate formed at thecentral portion of the seal ring by making the thickness of apredetermined region of the seal ring in the range more than 0 degreeand not more than 165 degrees, favorably not less than 5 degrees normore than 90 degrees, and more favorably not less than 5 degrees normore than 50 degrees or by making the thickness of a predeterminedregion of the seal ring having a central angle not less than 20 degreesnor more than 130 degrees smaller than that of the position opposed tothe abutment portion. The present invention is based on this knowledge.

FIGS. 1A and 1B show the state in which the inner diameter of the sealring whose thickness and width do not change in its entire circumferenceis expanded. FIG. 1A is a sectional view in a diametrical direction.FIG. 1B is a sectional view taken along a line B-B of FIG. 1A. The sealring 1 is supported on the peripheral surface of a tapered jig 4 atthree points, namely, at abutments 2 a, 2 b thereof and a position 3 athereof opposed to the abutments 2 a, 2 b. The seal ring 1 is and has aconstant thickness t and a constant width W throughout the entirecircumference thereof as shown in FIG. 1B.

By using the finite element method, the present inventors analyzed theconstruction of the seal ring 1 having a configuration shown in FIG. 7by examining the magnitude of a strain generated therein. To do so, withthe seal ring 1 fitted on a tapered jig 4, the abutments 2 a, 2 b areexpanded to a position of the tapered jig 4 at which the diameter was15.2 mm. The construction of the seal ring 1 was analyzed by setting thewidth of the seal ring to 1.4 mm, 1.5 mm, and 1.6 mm. FIG. 2 shows theresult.

In the abscissa axis of FIG. 2, the angle of an abutment portion, asshown in FIG. 1A, at the time when the abutments 2 a, 2 b were abuttedeach other was set to 180 degrees, whereas the angle of the position 3 aopposed to the abutments 2 a, 2 b was set to 0 degree.

The strain is generated to a higher extent gradually from 0 at 180degrees toward a peak value at 50 to 60 degrees and decreases toward 0degree. The tendency of the generated strain was approximately almostthe same when the width W of the seal ring was changed. The strain isgenerated symmetrically in a right-to-left direction.

According to the present invention, based on the results, the thicknessof a region of the seal ring where the magnitude of the generated strainis higher than that of a strain generated at a position (angle: 0degree) opposed to the abutment portion is made smaller than thethickness t at the position opposed to the abutment portion. By settingthe thickness of the seal ring in this manner, when the inner diameterof the seal ring is expanded by using the tapered jig, the innerdiameter of the seal ring is expanded mainly in the thin portion.Therefore it is possible to prevent the seal ring from being broken atthe gate formed at the central portion of the seal ring.

An embodiment of the seal ring of the present invention is describedbelow with reference to FIG. 3A and FIG. 3B. FIG. 3A is a plan view ofthe seal ring made of resin. FIG. 3B is a sectional view taken along theline A-A of FIG. 3A.

The seal ring 1 has an abutment portion 2 consisting of abutments 2 a, 2b confronting each other. The seal ring 1 rectangular in its sectionalconfiguration has a thickness t and a width W. A gate serving as a resininjection opening is formed at a position 3 a opposed to the abutmentportion 2. The seal ring 1 is divided into a thick portion t₁ and a thinportion t₂ formed along the circumference. The thickness of the thickportion t₁ is equal to that of the abutment portion 2 and that of theposition 3 a opposed to the abutment portion 2. The outer diameter R ofthe seal ring 1 in the thick portion t₁ is equal to that in the thinportion t₂. Thus the thin portion t₂ is thinly formed by cutting off theinner peripheral portion of the seal ring 1. Supposing that the angle ofthe abutment portion 2 of the seal ring 1 is 180 degrees and the angleof the position 3 a opposed to the abutment portion 2 is 0 degree, theregion in which the thin portion t₂ is formed is set to more than 0degree and not more than 165 degrees, and favorably in the range 5degrees nor more than 90 degrees. Because the radial length of the gateis frequently not less than 0.5 mm in injection molding, it ispreferable to set the angle of the thin portion t₂ to not less than fivedegrees to hold a circumferential length V for the thick portion wherethe gate is disposed. If the angle of the thin portion t₂ is more than165 degrees, it is difficult for the seal ring to be supported by themating shaft.

As the circumferential length V of the thick portion of the gate becomessmaller, it becomes increasingly easy to prevent the seal ring frombeing broken when the seal ring is fitted on the shaft. Therefore it ispreferable to set the angle β of circumference to not more than 30degrees. If the angle β of circumference is more than 30 degrees, it isimpossible to sufficiently prevent the breakage of the seal ring at thegate. It is preferable to set the angle β of circumference to not lessthan five degrees owing to the presence of the radial length of thegate.

In the above-described angle range, the central angle α of the region inwhich the thickness of the seal ring is made thin is not less than 20degrees nor more than 130 degrees. If the central angle α is out of thisrange, there is a possibility that the relationship between the shaftand seal ring cannot be fixed and that the shaft becomes eccentric froma cylinder.

As a preferable example of the angle for making the thickness t of theseal ring smaller than that of the portion 3 opposed to the abutmentportion in the seal ring shown in FIGS. 3A and 3B, the angle β ofcircumference is in the range of 5 to 30 degrees, and the central angleα is not less than 20 degrees nor more than 85 degrees.

The thickness of the region of the seal ring having the smallerthickness is 60 to 95% of the thickness of the abutment portion or thethickness of the portion opposed to the abutment portion. If thethickness of the region of the seal ring having the smaller thickness isless than 60% of the thickness of the abutment portion or the portionopposed to the abutment portion, there is a fear that an abnormalfriction occurs owing to an increase of a pressure applied to theportion of contact between the surface of the seal ring and the ringgroove of the shaft and that the oil-sealing performance of the sealring deteriorates.

It is preferable that the region of the seal ring having the smallerthickness is formed symmetrically in the right-to-left direction withrespect to the position opposed to the abutment portion, because thisconstruction accomplishes a favorable balance in the flow of resin in amolding operation. The region of the seal ring having the smallerthickness is not necessarily symmetrical in the right-to-left directionwith respect to the position opposed to the abutment portion. Thethickness of the seal ring may be changed stepwise or successively. Thethickness of the seal ring is adjusted not at the outer peripheral sidethereof but at the inner peripheral side thereof. If the thickness ofthe seal ring is adjusted at the outer peripheral side thereof, it isimpossible to keep oil-sealing performance. Thus the seal ring cannot beused.

The region of the seal ring having the smaller thickness may be formedby injection molding or by mechanically processing a conventional sealring having a constant thickness.

As the configuration of the abutment of the seal ring, straight cut andstep cut can be adopted. The step cut is more favorable than thestraight cut, because the former is superior to the latter in itsoil-sealing performance.

If the region of the seal ring having the smaller thickness is formedsymmetrically in the right-to-left direction with respect to theposition opposed to the abutment portion, it is preferable to form thegate at the position opposed to the abutment portion or in theneighborhood thereof in injection molding. Thereby a favorable balancecan be obtained in the flow of resin in a molding operation and furthera high productivity can be obtained because plural production ispossible in one shot.

By disposing the gate at the inner peripheral side of the seal ring, theneed for performing post-processing can be eliminated.

Although a side gate can be adopted as the form of the gate, a pin gateand a submarine gate are preferable because the pin gate and thesubmarine gate eliminate the need for performing post-processing.

The present invention is applicable to seal rings of various sizes andparticularly effectively applicable to a seal ring having an innerdiameter not more than 20 mm because the seal ring whose inner diameteris not more than 20 mm is liable to be broken when it is fitted on arotary shaft. In the seal ring whose inner diameter is more than 20 mm,a strain is generated to a comparatively low extent at the positionopposed to the abutment portion in fitting the seal ring having an innerdiameter more than 20 mm on the rotary shaft. Thus the seal ring whoseinner diameter is more than 20 mm does not have the problem of breakage.

In addition to the neighborhood of the position opposed to the abutmentportion disposed at the center of a molded product, the gate may bedisposed in a region having a low extent of strain shown in FIG. 2. Thatis, the gate may be formed at a position near any one of the abutmentsspaced by not less than 90 degrees from the position opposed to theabutment portion, supposing that the abutment portion is set to 180degrees and the position opposed to the abutment portion is set to 0degree. Which of the two abutments is selected depends on the magnitudeof a strain generated thereat.

When the seal ring is small, i.e., when the inner diameter thereof isnot more than 20 mm, troubles occur little in a molding operation owingto the difference in the flow length of resin between the left-hand sideand right-hand side with respect to the gate. However, a burr is formedowing to the difference in the flow length of the resin between theleft-hand side and right-hand side with respect to the gate. Further theamount of the charged resin is short at the side where the flow lengththereof is long. In this case, by spacing the gate position at a certaininterval from the position opposed to the abutment portion and forming aresin reservoir at the side where the flow length of the charged resinis short, it is possible to prevent an excess resin from flowing to theresin reservoir in the injection molding and prevent an over-chargingfrom occurring at the side where the flow length of charged resin isshort. The inlet portion of the resin reservoir is so configured thatthe resistance to the flow of the resin into the resin reservoir ishigher than the resistance to the flow of the resin into the sealingportion. Thus the charging of the resin into the resin reservoir isdelayed behind the charging thereof into the sealing portion. Therebythe size of the resin reservoir can be made smaller than the differencebetween the flow length of the resin into the resin reservoir and thatof the resin into the sealing portion. By setting the size of the resinreservoir in such a way that the resin reservoir and the sealing portionare charged simultaneously and completely with the resin, it is possibleto suppress generation of a burr formed by over-charging of resin andgeneration of a molding sink that is generated by shortage of afollow-up pressure.

In the method of producing the seal ring made of resin by spacing thegate position at a certain interval from the position opposed to theabutment portion, molding is so performed that the sealing portion andthe resin reservoir portion are simultaneously and completely chargedwith the resin in an injection molding process. Otherwise, molding is soperformed that the sealing portion is completely charged with the resin,whereas the resin reservoir portion is incompletely charged therewith.Thus the seal ring of the present invention is excellent in itsmechanical strength and dimensional precision.

Further, the inlet portion of the resin reservoir is so configured thatthe size of the resin reservoir can be made small. Thus the resin sealring of the present invention is excellent in easy post-processing andhigh productivity. And also down-sizing of the rein reservoir makessmall seal ring possible to be produced in the diameter not more than 20mm.

One example of the seal ring made of resin according to the presentinvention is described below with reference to FIG. 5. FIG. 5 is a planview showing the body of a seal ring and the position of a gate and thatof a resin reservoir formed in injection molding.

A seal ring 1 has an abutment portion 2 consisting of abutments 2 a, 2 bconfronting each other and a gate mark 5 a where the gate was joinedwith a portion of the seal ring 1, when injection molding was performed.As the configuration of the abutments 2 a, 2 b, straight cut and stepcut can be adopted. The step cut is more favorable than the straight cutbecause the former is superior to the latter in its oil-sealingperformance.

A resin reservoir 6 is formed on the inner peripheral surface of theseal ring 1 between the abutment 2 a and the gate mark 5 a in theinjection molding. The resin reservoir 6 is formed through a resinreservoir inlet portion 7 provided to adjust the amount of resin flowinginto the resin reservoir 6.

The gate 5 and the resin reservoir 6 are removed before a finishedproduct of the seal ring 1 is obtained.

As shown in FIG. 2, the strain increases gradually from 0 at 180 degreesto a peak value at about 60 degrees and decreases toward 0 degree. Theresult shown in FIG. 2 indicates that by forming the gate at a positionforming not less than 90 degrees from the position opposed to theabutment portion and favorably not less than 120 degrees therefrom, itis possible to reduce the amount of a strain generated at the gateposition and hence greatly improve the fittability of the seal ring onthe shaft. It has been found that at a position less than 90 degrees,the fittability can be hardly improved, even though the gate position isshifted from the position 3 a opposed to the abutment portion 2 orrather the fittability deteriorates (worst at the position of about 60degrees).

Based on the above-described knowledge and the examples described later,the angle γ formed between the gate 5 and the position 3 a opposed tothe abutment portion 2 is set to 90°≦180° and favorably 120°≦γ<150°. Ifthe angle γ is not smaller than 150 degrees, there is a too largedifference in the flow length of charged resin between the left-handside and right-hand side with respect to the gate.

Although the side gate can be adopted as the form of the gate 5, the pingate and the submarine gate are preferable because the pin gate and thesubmarine gate eliminate the need for performing post-processing. Thegate 5 can be formed at both the inner peripheral side of the seal ring1 and the peripheral side thereof. But it is preferable to form the gate5 at the inner peripheral side thereof. Thereby the seal ring 1 hassuperior oil-sealing performance and the need for performingpost-processing can be eliminated.

The resin reservoir 6 is provided to adjust the amount of resin chargedfrom the abutment 2 a to the gate mark 5 a and the amount of the resincharged from the abutment 2 b to the gate mark 5 a so that both amountsare approximately equal to each other. Therefore the resin reservoir 6is formed at a position, between the abutment 2 a and the gate mark 5 a,where the flow length of the charged resin is short and hence anovercharge of resin occurs. The central angle δ of the seal ring withrespect to the position 3 a opposed to the abutment portion 2 is notlimited to any specific angle, provided that the resin reservoir 6 isdisposed at the side where the flow length of the charged resin isshort. But preferably the central angle δ is in the range of 0 degree to90 degrees.

Consequently it is possible to have a favorable balance of a flow ratebetween the left-hand side and right-hand side with respect to the gate5 and suppress generation of a burr. Hence the seal ring of the presentinvention is excellent in its mechanical strength and dimensionalprecision.

The resin reservoir 6 is set to a size larger than the size which allowsthe seal ring 1 and the resin reservoir 6 to be simultaneously andcompletely charged with resin in a follow-up pressure applicationprocess (secondary injection process) to be performed subsequently to aninjection process (primary injection process). This is because if theresin reservoir 6 is charged completely with the resin faster than theseal ring 1, an unbalanced charging of the resin occurs. Thereby thereis a fear that a burr is generated at the side where the flow length ofthe charged resin is short. Hence there is interference with theoil-sealing performance of the seal ring 1.

The smaller the resin reservoir 6, the more favorable in recycling theseal ring. In the small seal ring having not more than 20 mm in itsinner diameter, the space of a die corresponding to the inner peripheralside is very small. Thus it is necessary to make the volume of the resinreservoir small in forming the resin reservoir at the inner peripheralside of the seal ring.

The resin reservoir 6 can be disk-shaped, cubic, rectangularsolid-shaped, spherical, and the like. Like the gate 5, the resinreservoir 6 can be formed at both the inner peripheral side of the sealring 1 and the peripheral side thereof. But it is preferable to form theresin reservoir 6 at the inner peripheral side thereof. Thereby the sealring 1 has superior oil-sealing performance and the need for performingpost-processing can be eliminated.

The inlet portion 7 of the resin reservoir is so configured that theresistance to the flow of resin into the resin reservoir 6 is higherthan the resistance to the flow of the resin into the sealing portion inan injection molding operation. The volume necessary for the resinreservoir 6 can be adjusted in dependence on the resistance to the flowof the resin into the inlet portion 7. That is, a volume necessary forthe resin reservoir 6 can be reduced by making the resistance to theflow of the resin into the inlet portion 7 large. In the case where theseal ring 1 has a configuration shown in FIG. 5, as the diameter W₁ ofthe inlet port of the resin reservoir becomes smaller and the length W₂of the inlet portion of the resin reservoir becomes larger, theresistance to the flow of the resin into the inlet portion 7 becomesincreasingly high, and the volume of the resin reservoir 6 becomesincreasingly small. The inlet portion 7 of the resin reservoir is cutoff from the seal ring 1 after the injection molding finishes. Thus itis preferable that the inlet portion 7 is formed to have the shape of apin gate or a submarine gate to facilitate post-processing.

It is known that when the resistance to the flow of the resin into theproduct portion is too high, a burr is generated on a product. If theresistance to the flow of the resin into the inlet portion 7 is higherthan the resistance to the flow of the resin into the product portion,the flow of the resin into the resin reservoir 6 is obstructed and theresistance to the flow of the resin into a product portion is high.Consequently there is a fear that a burr is generated on the productportion. Accordingly, it is preferable that the inlet portion 7 of theresin reservoir is so configured that the resistance to the flow of theresin into the inlet portion 7 satisfy the above-described condition andan equation 1 shown below.Inflow resistance when burr is generated>Inflow resistance at inletportion of resin reservoir≧Inflow resistance at sealingportion  Equation 1

The minimum volume of the resin reservoir 6 and the inlet portion 7 ofthe resin reservoir are determined by injection molding to be performedby using a die having the gate at a desired position (γ>90 degrees) andthe resin reservoir 6 formed thereon through the inlet portion 7 havinga predetermined configuration and by carrying out the following method.

(1) Molding is performed in an injection condition in which not lessthan 90% of the seal ring portion is charged with resin in a primaryinjection process in which a follow-up pressure is not used. Otherwise,the configuration of the inlet portion 7 of the resin reservoir isadjusted in a fixed injection condition to charge not less than 90% ofthe seal ring portion with resin.

(2) The volume of the resin charged in the resin reservoir 6 is measuredwhen the step (1). The charged volume of the resin reservoir 6 can besimply measured by using the density of the resin from the chargedweight of the resin reservoir 6.

(3) A minimum volume (100%) of the resin reservoir 6 is computed,supposing that the volume of the resin reservoir 6 measured in the step(2) is equivalent to 90% of the minimum volume of the resin reservoir 6.

FIG. 6 shows a flowchart of the method of manufacturing the seal ringmade of resin of the present invention. The manufacturing methodincludes a molding preparing step 8, an injection molding step 9, and amolded product take-out step 10. The injection molding step 9 and themolded product take-out step 10 can be carried out by using knownprocesses. For example, as the injection molding step 9, it is possibleto use a clamping process of clamping a male die and a female die sothat they withstand a pressure in an injection operation. As the moldedproduct take-out step 10, it is possible to use a process of opening adie at a predetermined speed and further an ejection process of takingout a molded product which has closely adhered to the die, by utilizinga hydraulic pressure or the like.

The injection molding step 9 is the step of performing injection moldingby using a die having a resin reservoir, provided through an inletportion thereof at a position between a gate, for injection molding use,which is spaced at a given interval from the position opposed to anabutment portion and one abutment nearer to the gate than the otherabutment in the circumferential distance of the seal ring. In theinjection molding step 9, the size of the resin reservoir and theconfiguration of the inlet portion of the resin reservoir are adjustedto simultaneously and completely charge the sealing portion and theresin reservoir portion with resin; or melted resin is so injected as tocharge the sealing portion completely with the resin and charge theresin reservoir portion incompletely with the resin.

More specifically, the injection molding step 9 includes an injectionstep 9 a and a follow-up pressure application step 9 b to be performedsubsequently to the injection step 9 a. In the follow-up pressureapplication step 9 b, the resin of the seal ring is cooled, with thefollow-up pressure being applied thereto to completely charge thesealing portion with the resin. In the follow-up pressure applicationstep 9 b, melted resin is added as necessary in correspondence to acontracted amount of the resin when the resin is cooled and solidified.After the injection molding step 9 finishes, the molded product take-outstep 10 is performed. In this manner, a molded product of the seal ringis obtained.

As described above, the smaller the resin reservoir, the better. Thus itis preferable that when the sealing portion is completely charged withthe resin in the follow-up pressure application step 9 b, the resinreservoir and the sealing portion are completely and simultaneouslycharged with the resin.

In the case where the resin reservoir is incompletely charged with theresin when the sealing portion is completely charged therewith, thesealing portion is cooled at a high speed because the width of thesealing portion is short, namely, 2 mm or less. Because the inletportion of the resin reservoir has a large specific area, the inletportion is cooled at a high speed and solidified faster than the productportion. Thus the follow-up pressure is uniformly applied to the productportion. Therefore a molding sink is not generated in the productportion.

After the injection molding step 9 finishes, the molded product take-outstep 10 is performed to obtain a molded product of the seal ring.Annealing treatment can be conducted on the molded product.

The manufacturing method of the present invention is applicable to sealrings having various sizes and preferably to the production of the sealring having an inner diameter of not more than 20 mm. This is because inthe seal ring having an inner diameter of more than 20 mm, the magnitudeof a strain generated by expansion of the inner diameter iscomparatively low when the seal ring is fitted on the shaft, even thoughthe seal ring has the gate at the position opposed to the abutmentportion. On the other hand, the seal ring having an inner diameter ofnot more than 20 mm and especially not more than 18 mm has a strain of ahigh magnitude and is broken while it is being expanded.

It is possible to use a resin material for the seal ring in the presentinvention, provided that it has heat resistance at temperatures at whichthe seal ring is used and a sufficient mechanical strength. Thus thefollowing resins can be used: polyarylene sulfide resin such aspolyphenylene sulfide (PPS) resin; polyimide resin such as polyetherimide resin, polyamide-imide (PAI) resin, thermoplastic polyimide (TPI)resin; aromatic polyester resin such as fully aromatic polyester;polyamide resin such as nylon 46, nylon 9T; polycyanoaryl ether resinsuch as polyether nitrile resin; and polyether ketone resin such aspolyether ketone (PEK) resin and polyether ether ketone (PEEK) resin. Itis possible to use a mixture of these resins, for example, a polymeralloy of the PPS resin and the PAI resin and a composite resin of thePEEK resin and polybenzimidazole resin.

The PEEK resin, the PEK resin, and the TPI resin are most favorable ofthese resin materials.

It is possible to add the following materials to the resin material:fibrous reinforcing materials such as carbon fiber (CF) and glass fiber;spherical fillers such as spherical silica and spherical carbon; scalyreinforcing materials such as mica and talc; and fine fibrousreinforcing materials such as a whisker of potassium titanate. It ispossible to add solid lubricants such as PTFE resin, graphite, andmolybdenum disulfide to the resin material. It is possible to addsliding reinforcing materials such as calcium phosphate and calciumsulfide to the resin material. These materials can be added to the resinmaterial singly or in combination. It is possible to conduct annealingtreatment such as heat treatment after injection molding is performed toenhance crystallinity index of the seal ring made of the resin materialand hence improve heat resistance and mechanical strength thereof.

The seal ring of the present invention is obtained by molding a resincomposition containing polyether ketone, selected from among theabove-described resin materials, serving as the matrix resin thereof anda predetermined amount of a spherical carbon material, whose mainconstituent element consists of carbon, added to the matrix resin.

As the polyether ketone resin, PEK resin and PEEK resin having astructure in which aromatic rings are connected with ether groups andketone groups are available. The PEEK resin is more favorable than thePEK resin because the former is excellent in its heat resistance,mechanical strength, self-lubricity, and flexibility. The tensileelongation of the PEEK resin is not less than 50%.

The chemical formula 1 shows an example of the repeating unit ofpolyether ketone resin. It is possible to use a copolymer of therepeating unit shown by the chemical formula 1 and the repeating unitshown by the chemical formula 2.

The polyether ketone resins are crystalline. The maximum crystallizationpercentage of the PEEK resin is as high as 48%. According to the presentinvention, the following polyether ketone resin are preferable:VICTREX-PEK220G (produced by Victrex Inc.), VICTREX-PEEK150P, 380P, and450P (all produced by Victrex Inc.), HOSTATEC (produced by HoechstInc.), and ULTRA PEK-A1000 (produced by BASF Aktiengesellschaft).

In the polyether ketone resin serving as the matrix resin of the presentinvention, grades having different molecular weights may be blended.Further resin superior in its heat resistance may be added to thepolyether ketone resin, provided that the function of the presentinvention is not deteriorated thereby.

As the crystalline resin of the above-described other resins, it ispossible to use the following resins whose melting points are not lessthan 250° C.: aromatic polyamides such astetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA),ethylene-tetrafluoroethylene copolymer (ETFE), polyamide 66 (PA66),polyamide46 (PA46), aromatic polyamide6 (PA6T), and aromatic polyamide9(PA9T); aromatic polyesters such as polyethylene terephthalate (PET),and liquid crystal polyester (LCP); polyarylene sulfides (PAS)represented by polyphenylene sulfide (PPS); thermoplastic polyimide(TPI), and polybenzimidazole (PBI).

The spherical carbon materials of the present invention contain carbonas the main constituent element thereof. The preferable spherical carbonmaterials have a true specific gravity not less than 1.3 and less than2.0 and are not graphitized much. Carbon black, meso-carbon micro-bead,spherical graphite, and the like having a high graphitization and a truespecific gravity not less than 2.0 have cleavage tendency. Thus thesegraphitized materials do not provide the seal ring with a sufficientwear resistance. The spherical carbon material having a true specificgravity less than 1.3 and carbonized insufficiently has difficulty indisplaying its function and hence does not allow the seal ring to have asufficient wear resistance.

As the spherical carbon material, spherical glass carbon and carbonblack having a low extent of aggregation are available.

As the spherical glass carbon, Belpearl C-2000 (produced by Kanebo Inc.)formed by carbonizing spherical phenol resin particles by heat treatmentand Nicabeads (produced by Nippon Carbon Inc.) are available. As thecarbon black having a low extent of aggregation, carbon black #3030B(produced by Mitsubishi Chemical Corp.) produced by using oil furnacemethod is available.

Supposing that the addition amount of the spherical carbon material isV₂ (volume %) and that the average particle diameter of the sphericalcarbon material is d (Mm), the spherical carbon material is used in sucha way as to satisfy the following equation 2.0.76In d+5.7<V ₂<1.27 In d+11.20.03<d≦50  Equation 2

The equation 2 was determined based on results of the inner diameterexpansion test and the frictional wear test, described later in“examples of the present invention”, which were conducted on seal ringsobtained by injection-molding a resin composition for lubricants in oilcontaining the spherical carbon material essentially. The left side ofthe equation 2 was obtained from the relationship between the particlediameter of the spherical carbon material as well as its mixing amountand the wear resistance of the seal ring based on the frictional weartest. The right side of the equation 2 was obtained from therelationship between the particle diameter of the spherical carbonmaterial as well as its mixing amount and the flexibility of the sealring based on the inner diameter expansion test.

When the mixing amount V₂ of the spherical carbon material is not morethan the value of the left side of the equation 2, it is impossible toobtain a sufficient wear resistance demanded for the seal ring. Furtherbecause the amount of additives is small, a molding sink or a burr tendsto be generated. Thereby it is necessary to perform post-processing oftreating the burr and hence there is a possibility that the seal ring isincapable of satisfying oil-sealing performance.

When the mixing amount V₂ of the spherical carbon material is more thanthe value of the right side of the equation 2, it is not sufficientlyflexible. The seal ring may be broken in fitting the seal ring on theshaft. In the case where spherical particles having an average diameterd not more than 0.1 μm are used, they are thickened to a very highextent. Thus it is very difficult to mold the resin material for theseal ring or there is a possibility that the resin material cannot bemolded.

The average diameter d of the spherical particle is set to favorably notless than 0.03 μm and less than 50 μm and more favorably not less than0.04 μm nor more than 30 μm. If the average diameter d of the sphericalparticle is less than 0.03 μm or not less than 50 μm, wear resistance ofthe seal ring may be unstable. Particles whose average diameter d isless than 0.03 μm have a very strong cohesion. Thus they are incapableof making a stable uniform dispersion. On the other hand, particleswhose average diameter d is not less than 50 μm are too large for theunit of wear. Thus they are incapable of imparting a uniform wearresistance to the seal ring.

The following molding method may be carried out to obtain the seal ring:after materials such as the resin composition for lubricants in oil, andthe spherical carbon material for the seal ring are mixed with oneanother by a mixer such as a Henschel mixer, a tumbler mixer, a ballmixer, a ribbon blender, a Loedige mixer, the components are meltinglykneaded by a biaxial kneader or a mono-axial kneader to form a pellet.Thereafter the pellet is injection-molded by a conventional injectionmolding method. It is possible to conduct annealing treatment such asheat treatment after the injection molding is performed to enhancecrystallinity index of the seal ring and thus improve its heatresistance and mechanical strength thereof.

The following additives may be added to the resin material in additionto the spherical carbon material: inorganic additives such as carbonfiber, glass fiber, ceramic fiber, glass beads, glass balloon, mica;solid lubricants such as graphite, PTFE resin, and molybdenum disulfide;thermal conductivity-imparting materials such as metal oxides and metalfibers; release agents, thermal stability-improving materials; variouswhiskers; and thermosetting resin. These materials can be added to theresin material singly or in combination. Surface treatment such ascoupling treatment may be made on these additives. The PTFE resin showsreleasability from a die in injection molding and is a preferableadditive.

Side feeding may be adopted when these additives and the resin materialare kneaded by a biaxial kneader.

The gate position is not limited to a specific position in producing theseal ring of the present invention by injection molding. But it ispreferable to dispose the gate position at the inner peripheral side ofthe seal ring. Thereby it is possible to secure oil-sealing performanceand eliminate the need for performing post-processing operation. It isalso preferable to dispose the gate in the neighborhood of the portionopposed to the abutment portion in consideration of a favorable balancein the flow of resin in injection molding. Supposing that the angle ofthe abutment portion of the seal ring consisting of abutmentsconfronting each other is 180 degrees and the angle of the portionopposed to the abutment portion is 0 degree, it is preferable to disposethe gate in the range of 0 degree to ±15 degrees at the inner diameterside of the seal ring.

As the configuration of the abutment, it is possible to adopt anydesired configurations such as straight cut, angle cut, step cut, andthe like. The step cut is most favorable because the step cut allows theseal ring to have superior oil-sealing performance.

Examples 1 through 4 and Comparison Examples 1 through 4

15 wt % of carbon fiber (CF) (HTA-CMF-0160-OH produced by Toho RayonInc.) and 15 wt % of PTFE KTL-610 produced by Kitamura Inc. were addedto 70 wt % of PEEK resin (PEEK 150P produced by Victrex Inc.). Afterthese components were mixed with one another by using a Henschel mixer,resin pelletized by using a biaxial kneader was used as the material,for the seal ring, to be injection-molded.

A die configured as shown in table 1 was prepared. Using the die, thematerial was injection-molded to obtain a seal ring whose thin portionsare symmetrical with respect to the position opposed to the abutmentportion shown in FIG. 3A. The diameter of the gate of each of theexamples and the comparison examples was set to 0.6 mm.

Whether each seal ring passed the examination was evaluated by measuringthe expansion amount of the inner diameter thereof by using a taperedjig having a length of 30 cm, a diameter of 11 mm at a smaller-diameterside thereof, and a diameter of 17.5 mm at a larger-diameter sidethereof. The seal ring was fitted on the tapered jig from thesmall-diameter side. When the seal ring was broken or cracked, the innerdiameter of the seal ring was measured. In the process of fitting sealrings on shafts respectively in mass production, a seal ring having anouter diameter of 15 mm cannot be frequently fitted on a shaft when theexpansion amount of the inner diameter of the seal ring is less than15.3 mm. Therefore the seal ring in which the expansion amount of theinner diameter was not less than 15.4 mm was marked by “G” (means“good”, same as below “G”), whereas the seal ring in which the expansionamount of the inner diameter was not more than 15.4 mm was marked by “NG(means “not good”, same as below “NG”)”. Table 1 shows the result. Intable 1, “normal thickness” indicates t₁ shown in FIG. 3B, and“thickness of thin portion” indicates t₂ shown in FIG. 3B.

TABLE 1 Example Comparison example 1 2 3 4 1 2 3 4 Outer diameter, mm 1515 15 15 15 15 15 15 Thickness of normal portion, mm 1.65 1.65 1.65 1.651.65 1.65 1.65 1.65 Angle of thin portion, degree 8-128 25-160 15-1008-30 none 90-146 16-113 50-70 Thickness of thin portion, mm 1.3 1.3 1.31.3 none 1.3 1.6 1.3 Expanded diameter, mm not less not less 17.3 15.614.5 14.5 15.1 14.6 than 17.5 than 17.5 Success or failure G G G G NG NGNG NG

As shown in table 1, the seal ring of each example was not broken whenthe expanded inner diameter thereof reached 15.4 mm.

According to the resin seal ring of the present invention, when theinner diameter of said seal ring is expanded, the thickness of theregion in which a strain is generated in a higher magnitude than astrain generated at said gate position is set smaller than that of thegate position. Therefore the seal ring can be prevented from beingbroken when it is fitted on a rotary shaft. Particularly, the seal ringwhose inner diameter is not more than 20 mm can be prevented from beingbroken when it is fitted on the rotary shaft. Therefore it is possibleto improve productivity in the process of fitting the seal ring on therotary shaft.

Furthermore since it is possible to dispose the gate at the positionopposed to the abutment portion and design the seal ring in such a waythat the configuration thereof is symmetrical in the right-to-leftdirection with respect to the gate. Therefore an unbalanced charging ofthe resin can be avoided in the molding process. Further a weld portionis not generated. Therefore the seal ring is excellent in its qualityand productivity.

Examples 5 through 8 and Comparison Examples 5 through 7

The resin material of each of the examples 5 through 8 and thecomparison examples 5 through 7 was prepared by adding 15 wt % of carbonfiber HTA-CMF-0160-OH (produced by Toho Rayon Inc.) and 15 wt % of PTFEKTL-610 (produced by Kitamura Inc.) to 70 wt % of PPEK 150P (produced byVictrex Inc.). After these materials were mixed with one another byusing a Henschel mixer, the mixture pelletized at 360° C. by using abiaxial kneader was injection-molded at a resin temperature of 380° C.and a die temperature of 180° C.

The seal ring die used in the examples and the comparison examples wasprovided with a resin reservoir. The outer diameter of the die was 15mm. The gate position could be disposed at any desired positions of theinner peripheral side. A telescopic construction was adopted for theresin reservoir to alter the volume thereof. The position of the resinreservoir was fixed to a position of δ=20 degrees. Molding operation wasperformed by changing the gate position γ, the diameter W₁ of the inletport of the resin reservoir, the length W₂ of the inlet portion of theresin reservoir, and the volume V₁ of the resin reservoir.

After the molded portion of the resin reservoir was removed from theseal ring by processing, annealing treatment was conducted inpredetermined conditions.

Whether or not a burr or a molding sink was generated in the productportion was checked to evaluate the moldability of each seal ring. Toevaluate the fittability of each seal ring on the shaft, the expansionamount of the inner diameter thereof was measured by using a tapered jighaving a length of 30 cm, a diameter of 11 mm at a smaller-diameter sidethereof, a diameter of 17.5 mm at a larger-diameter side thereof.

The seal ring which had a burr or a molding sink generated thereon wasmarked by “NG”, whereas the seal ring which had no problems in terms ofmolding was marked by “G”.

To measure the expansion amount of the inner diameter, the seal ring wasfitted on the tapered jig from the small-diameter side of the taperedjig. When the seal ring was broken or cracked, the inner diameter of theseal ring was measured.

As the general judgement, the seal ring in which the total of theinitial inner diameter of the seal ring and the expanded amount thereofwas not less than 15.4 mm was marked by “G”, whereas the seal ring inwhich the total of the initial inner diameter of the seal ring and theexpanded amount thereof was not more than 15.4 mm was marked by “NG”. Infitting the seal ring on the shaft, the seal ring is expanded more thanthe outer diameter thereof. Thus as the standard by which the expansionamount of the inner diameter is judged, 15 mm equal to the outerdiameter of the seal ring was adopted. Table 2 shows the result of theevaluation.

TABLE 2 Comparison Example example 5 6 7 8 5 6 7 Gate position α, degree100 120 120 140 0 60 120 Diameter of inlet port of resin 0.6 0.4 0.4 0.3— 0.6 0.4 reservoir W₁, mm Length of inlet portion of resin 3 3 5 3 — 33 reservoir W₂, mm Optimum volume of resin reservoir, 22 6 3 2 — 13 6mm³ Volume of resin reservoir actually 22 6 4 4 — 13 2 used, mm³Moldability G G G G G G NG Expanded inner diameter, mm 15.4 16.7 16.7more than 14.4 13.5 16.7 17.5 General judgement G G G G NG NG NG

In the examples 5 through 8, the gate position was far from the positionopposed to the abutments. The seal ring of each of the examples 5 and 6was formed by using a die provided with a resin reservoir having aminimum volume. The seal ring of each of the examples 7 and 8 was formedby using a die provided with a resin reservoir having a larger volume.Therefore the seal ring of each of the examples 5 through 8 wasexcellent in the moldability and the expansion amount of the innerdiameter thereof. Further the expansion amount of the inner diameter ofthe seal ring of each of the examples 5 through 8 was improved much morethan that of the seal ring of the comparison example 5 formed by using adie having a conventional configuration.

The seal ring of the comparison example 5 was formed by using aconventional resin reservoir-unprovided die having the gate positiondisposed at the position opposed to the abutments. There was no problemon the moldability but the total of the initial inner diameter of theseal ring and the expanded amount thereof was 14.4 mm. Thus the sealring was evaluated as “NG”.

The gate of the seal ring of the comparison example 6 was disposed atthe position indicated by γ=60 degrees. The volume of the resinreservoir was minimum. There was no problem on the moldability but theexpansion amount of the inner diameter of the seal ring was short. Thusthe seal ring was evaluated as “NG”.

The gate of the seal ring of the comparison example 7 was disposed atthe position indicated by γ=120 degrees. The volume of the resinreservoir was ⅓ of the minimum volume. Thus the resin reservoir wascompletely charged with resin in the injection process (primaryinjection process). When the injection molding finished, the resinadhered to the die and a burr was observed. Thus there was no problem onthe expansion amount of the inner diameter of the seal ring, but theseal ring was evaluated as “NG”.

The present invention is applicable to seal rings of various sizes andparticularly effectively applicable to a seal ring having an innerdiameter not more than 20 mm because the seal ring whose inner diameteris not more than 20 mm is liable to be broken when it is fitted on arotary shaft.

The materials used in the examples 9 through 14 and the comparisonexamples 8 through 16 are shown below. The parenthesized charactersdenote abbreviations shown in tables 3 though 5.

(1) Aromatic polyether ether ketone resin [PEEK1]

PEEK150P produced by Victrex Inc.

(2) Aromatic polyether ether ketone resin [PEEK2] PEEK450P produced byVictrex Inc.

(3) PTFE resin [PTFE]

KT-620 produced by Kitamura Inc.

(4) Spherical carbon material (carbon black) [CB1]

#3030B produced by Mitsubishi Kagaku Inc. (true specific gravity: 1.7 to1.9, configuration: spherical, average diameter: 55 nm)

(5) Spherical carbon material (micro-carbon beads) [CB2], MC-0520produced by Nippon Carbon Inc. (true specific gravity: 1.37 to 1.39,configuration: spherical, average diameter: 5 μm)

(6) Spherical carbon material (spherical amorphous carbon) [CB3],Pelpearl C-2000 produced by Kanebo Inc. (true specific gravity: 1.5 to1.6, configuration: spherical, average diameter: 2 μm)

(7) Graphite material (meso-carbon micro-bead) [GB1], MCMB-6-2800produced by Osaka Gas Inc. (true specific gravity: 2.1 to 2.2,configuration: spherical, average diameter: 6 μm)

(8) Spherical graphite material [GB1], LB-CG produced by Nippon GraphiteInc. (true specific gravity: 2.23 to 2.25, configuration:pseudo-spherical, average diameter: 20 μm)

(9) PAN carbon fiber (CF), Besphite HTA-CMF0160-OH (length of fiber:0.16 mm, diameter of fiber: 7 μm)

The materials were measured at the rates shown in tables 4 and 5 andmixed with one another by using a Henschel mixer. After the mixture waspelletized at 360° C. by using a biaxial kneader, the pellet wasinjection-molded at a resin temperature of 380° C. and a die temperatureof 180° C. to obtain each seal ring. As shown in FIG. 7, each seal ring1 had a gate mark 5 a at a position opposed to the abutment 2.

The addition amount of each of the spherical filler shown in theexamples 9 through 14 shown in table 4 was in the addable range based onthe equation 2 previously described. Table 3 shows the addable amount ofeach spherical filler.

TABLE 3 Average Lower limit Upper limit diameter d, of mixing of mixingμm amount, volume % amount, volume % CB1 0.055 3.5 7.5 CB2 5 6.9 13.2CB3 20 8.0 15.0 GB1 6 7.1 13.5 GB2 20 8.0 15.0

TABLE 4 Component, Example volume % 9 10 11 12 13 14 Matrix PEEK1 9692.5 87.5 90 87.5 67 PEEK2 — — — — — 22 Additive CB1  4 — — — —  6 CB2 — 7.5 12.5 — — — CB3 — — — 10 12.5 — GB1 — — — — — — GB2 — — — — — — CF —— — — — — PTFE — — — — —  5

TABLE 5 Component, Comparison example volume % 8 9 10 11 12 13 14 15 16Matrix PEEK1 75 98 90 95 82.5 95 80 90 90 PEEK2 — — — — — — — — —Additive CB1 —  2 10 — — — — — — CB2 — — —  5 17.5 — — — — CB3 — — — — — 5 20 — — GB1 — — — — — — — 10 — GB2 — — — — — — — — 10 CF 10 — — — — —— — — PTFE 15 — — — — — — — —

The inner diameter expansion test and the frictional wear test describedbelow were conducted on the seal ring of each of the examples and thecomparison examples Tables 6 and 7 show the results and generalevaluation of each test. FIG. 8 shows the relationship between theaverage particle diameter (μm) of the spherical carbon material added tothe resinous material of the examples 9 through 14 and the comparisonexamples 9 through 14 and the mixing amount (volume %) thereof. In FIG.8, the abscissa shows the average particle diameter (μm) of thespherical carbon material, and the ordinate shows the mixing amount(volume %) V₂ thereof.

Test for Examining Expansion of Inner Diameter

This test was conducted to evaluate the resistance of the seal ring tobreakage when the seal ring is fitted on the rotary shaft. In the test,a tapered jig having a length of 30 cm, a diameter of 11 mm at thesmaller-diameter side thereof, and a diameter of 17.5 mm at thelarger-diameter side thereof. A seal ring specimen was fitted on thetapered jig from the small-diameter side to expand the inner diameterthereof. When the seal ring specimen was broken or cracked, the innerdiameter of the seal ring was measured. The seal ring in which the totalof the initial inner diameter of the seal ring and the expanded amountwas not less than 15.4 mm was evaluated as “G”, whereas the seal ring inwhich the total of the initial inner diameter of the seal ring and theexpanded amount thereof was not more than 15.4 mm was evaluated as “NG”.In fitting the seal ring on a shaft, the seal ring is required to beexpanded more than the outer diameter thereof. Therefore as the standardby which the expansion amount of the inner diameter is judged, 15.4 mmequal to the outer diameter of the seal ring was adopted.

Test for Examining Frictional Wear

To evaluate the wear resistance, an in-oil frictional wear test wasconducted by using a ring specimen, which is made of resin compositionof the seal ring, having an outer diameter of 21 mm, an inner diameterof 17 mm, and a height of 3 mm and a ring-on-disk tester. The test wasconducted in oil for five hours and an atmospheric temperature of 100°C. by using a mating member, disk made of steel, rotating at a speed of64 m/minute and having a surface pressure of 5.5 MPa and a surfaceroughness of not less than Ra 0.8 μm. The oil used in the test wasautomatic transmission oil (ATF: Dexyron 2 produced by Showa Shell Inc.)The dynamic friction coefficient and the worn volume were measured. Thewear resistance was evaluated by the worn volume. The worn volume(condition of this test) of the seal ring of the comparison example 8composed of PEEK resin known as a sealing composition containing carbonfiber and PTFE which is a solid lubricant was used as the reference inmaking judgement. The seal ring having a worn volume less than 5 mm³ wasevaluated as “G”, whereas the seal ring having a worn volume not lessthan 5 mm³ was evaluated as “NG”.

As the judgement of the general evaluation, the seal ring evaluated as“G” in both the test of examining the expansion of the inner diameterthereof and the test for examining the frictional wear thereof wasmarked by “G”, whereas the seal ring evaluated as “NG” in either thetest of examining the expansion of the inner diameter thereof or thetest for examining the frictional wear thereof was marked by “NG”.

TABLE 6 Example 9 10 11 12 13 14 Inner diameter expansion test Expandeddiameter, mm 15.93 16.89 16.01 16.52 15.88 16.76 Evaluation G G G G G GFrictional wear test Dynamic friction coefficient 0.07 0.07 0.06 0.070.08 0.06 Worn volume, mm³ 3.1 3.8 3.6 3.7 3.7 2.8 Evaluation G G G G GG General evaluation G G G G G G

TABLE 7 Comparison example 8 9 10 11 12 13 14 15 16 Inner diameterexpansion test Expanded diameter, mm 14.46 more than 12.89 more than14.32 more than 14.13 15.91 16.52 17.5 17.5 17.5 Evaluation NG G NG G NGG NG G G Frictional wear test Dynamic friction coefficient 0.15 0.120.06 0.10 0.08 0.08 0.06 0.07 0.07 Worn volume, mm³ 3.0 35.8 2.7 31.43.3 34.2 3.0 7.9 11.6 Evaluation G NG G NG G NG NG NG NG Generalevaluation NG NG NG NG NG NG NG NG NG

As the spherical carbon material of the seal ring of the example 9,carbon black having a low extent of aggregation of particles whoseaverage diameter is 55 nm was used in the mixing range specified in thepresent invention. The spherical carbon material had excellentflexibility and wear resistance. Thus the seal ring was marked by “G” inthe general evaluation. The dynamic friction coefficient of the sealring was much lower than that of the seal ring of the comparison example8 containing the PEEK resin known as a sealing composition. This isbecause a preferable sliding state could be formed owing to excellentoil-maintaining performance of carbon displayed in the sliding portion.

As the spherical carbon material of the seal ring of the examples 10 and11, micro-carbon beads having an average particle diameter of 5 μm wasused in the mixing range specified in the present invention. Theparticle diameter of the spherical carbon material was much differentfrom that of the example 9. The seal ring of each of comparison examples10 and 11 had also excellent flexibility and wear resistance. Thus theseal rings were marked by “G” in the general evaluation. Like the sealring of the example 9, the dynamic friction coefficient of each sealring was also low.

As the spherical carbon material of the seal ring of the examples 12 and13, amorphous carbon having an average particle diameter of 20 μm wasused in the mixing range specified in the present invention. Theparticle diameter of the spherical carbon material was largest of thoseof the spherical carbon materials of all the examples. The seal ring ofeach of examples 12 and 13 had also excellent flexibility and wearresistance. Thus the seal rings were marked by “G” in the generalevaluation. Like the seal ring of the other examples, the dynamicfriction coefficient of each seal ring was also low.

The seal ring of the example 14 was composed of a mixture of two kindsof PEEK resins having different grades. As the spherical carbon materialof the seal ring, the same spherical carbon material as that of theexample 9 was added to the mixture of the PEEK in the mixing rangespecified in the present invention. The composition of the seal ringalso contained a small amount of PTFE as the release agent. Thecomposition displayed the effect of the present invention. The seal ringof the example 14 had also excellent flexibility and wear resistance.Thus the seal rings were marked by “G” in the general evaluation. Thedynamic friction coefficient of the seal ring was also low.

The seal ring of the comparison example 8 contained PEEK knowncomposition known as a sealing composition. Although the seal ring hadsuperior wear resistance, it had inferior flexibility. Thus the sealring was evaluated as “NG” in the test of examining the expansion of theinner diameter thereof. Therefore seal ring was evaluated as “NG” in thegeneral evaluation. The dynamic friction coefficient of the seal ringwas 0.15 which was highest.

As compared with the seal ring of the examples 9 and 14, the compositionof the seal ring of the comparison example 9 contained the sphericalcarbon material in an amount smaller than that the mixing rangespecified in the present invention. Because the seal ring had superiorflexibility, the seal ring was evaluated as “G” in the test of examiningthe expansion of the inner diameter thereof. Since the composition ofthe seal ring did not contain a predetermined amount of the sphericalcarbon material, a sufficient wear resistance was not imparted to theseal ring. Therefore seal ring was evaluated as “NG” in the test forexamining the frictional wear thereof and evaluated as “NG” in thegeneral evaluation.

As compared with the seal ring of the examples 9 and 14, the compositionof the seal ring of the comparison example 10 contained the sphericalcarbon material in an amount larger than that the mixing range specifiedin the present invention. The seal ring had inferior flexibility. Thusthe seal ring was evaluated as “NG” in the test of examining theexpansion of the inner diameter thereof. Although the seal ring hadsuperior wear resistance, it was evaluated as “NG” in the generalevaluation. The dynamic friction coefficient was low.

As compared with the seal ring of the examples 10 and 11, thecomposition of the seal ring of the comparison example 11 contained thespherical carbon material in an amount smaller than that the mixingrange specified in the present invention. Because the seal ring hadsuperior flexibility, the seal ring was evaluated as “G” in the test ofexamining the expansion of the inner diameter thereof. Since thecomposition of the seal ring did not contain a predetermined amount ofthe spherical carbon material, a sufficient wear resistance was notimparted to the seal ring. Therefore seal ring was evaluated as “NG” inthe test for examining the frictional wear thereof and evaluated as “NG”in the general evaluation.

As compared with the seal ring of the examples 10 and 11, thecomposition of the seal ring of the comparison example 12 contained thespherical carbon material in an amount larger than that the mixing rangespecified in the present invention. The seal ring had inferiorflexibility. Thus the seal ring was evaluated as “NG” (means “not good”,same as below “NG”) in the test of examining the expansion of the innerdiameter thereof. Although the seal ring had superior wear resistance,it was evaluated as “NG” in the general evaluation. The dynamic frictioncoefficient was low.

As compared with the seal ring of the examples 12 and 13, thecomposition of the seal ring of the comparison example 13 contained thespherical carbon material in an amount smaller than that the mixingrange specified in the present invention. Because the seal ring hadsuperior flexibility, the seal ring was evaluated as “G” in the test ofexamining the expansion of the inner diameter thereof. Since thecomposition of the seal ring did not contain a predetermined amount ofthe spherical carbon material, a sufficient wear resistance was notimparted to the seal ring. Therefore seal ring was evaluated as “NG” inthe test for examining the frictional wear thereof and evaluated as “NG”in the general evaluation.

As compared with the seal ring of the examples 12 and 13, thecomposition of the seal ring of the comparison example 14 contained thespherical carbon material in an amount larger than that the mixing rangespecified in the present invention. The seal ring had inferiorflexibility. Thus the seal ring was evaluated as “NG” in the test ofexamining the expansion of the inner diameter thereof. Although the sealring had superior wear resistance, it was evaluated as “NG” in thegeneral evaluation. The dynamic friction coefficient was low.

In the seal ring of the comparison example 15, the spherical carbonmaterial of the example 12 was replaced with high crystallinemeso-carbon micro-bead having a high graphitization. The mixing amountof the meso-carbon micro-bead was equal to that of the additive of theexample 12. Thus the mixing amount thereof was within the mixing rangespecified in the present invention. The seal ring had inferior wearresistance because the additive having a high graphitization was used.Although the seal ring had superior flexibility, it was evaluated as“NG” in the general evaluation. The dynamic friction coefficient waslow.

In the seal ring of the comparison example 16, the spherical carbonmaterial of the example 12 was replaced with natural graphitespherically treated. The mixing amount of the natural graphite was equalto that of the additive of the example 12. Thus the mixing amountthereof was within the mixing range specified in the present invention.Like the seal ring of the comparison example 15, the seal ring hadinferior wear resistance because the additive having a highgraphitization was used. Although the seal ring had superiorflexibility, it was evaluated as “NG” in the general evaluation. Thedynamic friction coefficient was low.

The range, shown by the equation 2, surrounded with the one-dot chainline of FIG. 8 was found from the results of the examples. By using theequation 2, it is possible to estimate the mixing amount (volume %) ofthe spherical carbon material having the degree of wear resistance andflexibility demanded for the seal ring from the average particlediameter (μm) of the spherical carbon material which is used as theadditive.

The resin seal ring of the present invention can be suitably utilized asan oil seal ring for use in a hydraulic mechanism of a vehicle and thelike.

1. A resin seal ring comprising abutments confronting each other and amark of a gate formed in an injection molding operation at a positionspaced at a certain interval from position opposed to said abutmentsabutting each other, wherein said mark of said gate is present in arange of not less than 90 degrees and less than 150 degrees in a centralangle of said seal ring with respect to said position opposed to saidabutments, supposing that an angle of said position opposed to saidabutments is 0 degrees, wherein said resin seal ring is formed byinjection molding using a die, said die having a resin reservoirprovided between said gate forming said gate mark and one abutmentnearer to said gate forming said mark than another abutment in acircumferential distance of said seal ring through a resin reservoirinlet portion, wherein said resin seal ring has a mark of said resinreservoir inlet portion, wherein said mark of said resin reservoir inletportion is between said mark of said gate and one of said abutments,wherein said inlet portion of said resin reservoir is configured so thata resistance to a flow of a resin into said resin reservoir is not lowerthan a resistance to a flow of said resin into a sealing portion in aninjection molding operation; and a size of said resin reservoir is notsmaller than a size that makes said resin reservoir and said sealingportion possible to be charged simultaneously and completely with saidresin in said injection molding operation, wherein said resin reservoiris provided at an inner diameter side of said seal ring; said mark ofsaid resin reservoir inlet portion being located at said inner diameterside of said seal ring.
 2. A seal ring according to claim 1, wherein aninlet portion of a resin reservoir is configured so that a resistance toa flow of a resin into said resin reservoir is not lower than aresistance to a flow of said resin into a sealing portion in aninjection molding operation and is pin gate-shaped or submarinegate-shaped.
 3. A seal ring according to claim 1, wherein an innerdiameter of said seal ring is not more than 20 mm.
 4. A seal ringaccording to claim 1, wherein a resin material of said seal ringconsists of one resin selected form among polyether ether ketone,polyether ketone, and thermoplastic polyimide.
 5. A seal ring accordingto claim 1, wherein said gate mark is present in a range of not lessthan 120 degrees and less than 150 degrees in a central angle of saidseal ring with respect to said position opposed to said abutments,supposing that an angle of said position opposed to said abutments is 0degree.
 6. A seal ring according to claim 1, wherein said inlet portionof said resin reservoir is configured so that a resistance to a flow ofa resin therein to satisfy an equation 1 shown below:Inflow resistance is generated when a burr is generated>Inflowresistance at inlet portion of resin reservoir≧Inflow resistance atsealing portion.  Equation 1